Batteries using various cell technologies (cell types) have been developed and are in widespread use. Two of the most common cell types are alkaline and nickel-cadmium (Ni-Cd). Other cell types include nickel-metal-hydride and various lithium technologies.
In many applications, batteries of differing cell types are interchangeable. For example, in many electronic products such as calculators, palmtop computers and the like, both alkaline and Ni-Cd type batteries can be used. In these circumstances, it is not always necessary to distinguish between cell types.
In other circumstances, however, cell type differentiation can be critical. One such critical circumstance is battery recharge. Some cell types, such as Ni-Cd, are rechargeable, while others, such as alkaline, are not. If a recharging current is applied to a non-rechargeable battery, the temperature of the battery increases rapidly, as does the internal pressure. Eventually, if recharging is continued, the battery will vent, resulting in leakage of caustic chemicals from the battery and possibly an explosion.
Many previous charging systems simply rely on the user, as directed by an owner's manual or warning notices, to prevent charging of an improper cell type. However, considering the probable consequences of charging improper cell types, it is desirable to protect the unwary user from charging batteries of the wrong cell type.
Some prior systems have relied on mechanical lock-out mechanisms for this purpose. Typical mechanical lock-out devices protect against the use of improper cell types by preventing installation in the system of batteries that do not have a particular size, shape or other mechanical feature. Only batteries having the particular mechanical feature can be installed. Typically, the mechanical feature is of non-standard design to avoid confusion with other battery types. However, the use of non-standard batteries often results in limited availability of suitable batteries to the public. The systems may therefore have difficulty in gaining public acceptance.
One prior method of differentiating between cell types of charging batteries is based on the temperature rise of non-rechargeable batteries. As noted above, non-rechargeable cell types increase in temperature when charged. A battery being recharged can therefore be identified as having a non-rechargeable cell type if it demonstrates an increase in temperature greater than would be demonstrated by a rechargeable cell type under the same charging conditions. A disadvantage to this method is that a considerable amount of time can elapse before non-rechargeable cell types rise to a temperature at which they can be identified as such. A considerable amount of time and electrical energy can therefore be expended in attempting to charge a battery before it is identified as non-rechargeable.
In accordance with the present invention, the cell type of a battery is determined by reference to characteristics of its electrical behavior during charging. Exemplary characteristics include the magnitude of the initial voltage rise, and the rate of initial voltage rise (each of which is greater for alkaline cells than Ni-Cd). Based on the outcome of this determination, the charging conditions can be changed (e.g. the charging current can be interrupted if the cell is determined to be a non-rechargeable type).
By the foregoing arrangement, the cell type of a battery can be determined quickly, and, if warranted, corrective steps can be taken to avoid damaging the battery and the associated equipment.
Additional features and advantages of the present invention will be made apparent from the following detailed description of a preferred embodiment, which proceeds with reference to the accompanying drawings.